Immersed membranes are used for extracting clean water (permeate) from a tank of contaminated water or mixed liquor. The membranes are often provided in the form of assembled modules, each module having many hollow fiber membranes extending between two headers for collecting permeate that passes through pores of the membrane walls into the lumina of the membranes. Streams of air bubbles may be provided in the tank to rub against the membranes for cleaning purposes. The air bubbles also help to create circulation patterns in the tank.
Although these features improve filtration along a central portion of the length of the fibers, a dead zone remains at either end of the fibers where sufficient cleaning of the fibers and circulation of the water does not occur, thereby causing the fibers at either end to become plugged or fouled by contaminants, and resulting in a corresponding decrease in the filtration capacity of the system. Presence of the dead zone is primarily caused by the headers themselves, which interfere with the flow of air bubbles and water circulation at either end of the fibers, and which inhibit movement of the fibers since the ends of the fibers are fixed to the headers.
Efforts have been made to overcome these drawbacks associated with two-header membrane modules by using single-header modules. However, single header modules involve various issues such as supporting the fibres, aerating the fibres and building groups of modules. There is a need for improvements relating to these and other issues.